The present invention concerns the fabrication of an inter-silicide capacitor for use in very large scale integrated (VLSI) circuits.
Various capacitor structures have been investigated for use in VLSI circuits. For example, in the prior art a poly-to-poly capacitor, a metal-to-poly capacitor and a metal-to-polycide capacitor have been suggested and used. See for example, C. Kaya, H. Tigelaar, J. Paterson, M. de Wit, J. Fattaruso, D. Hester, S. Kiriakai, K. Tan, F. Tsay, Polycide/Metal Capacitors for High Precision A/D Converters, IEDM, 1988, pp. 782-785.
The voltage linearity of a capacitor is the change in normalized capacitance of the capacitor per unit change in the voltage across the capacitor. A smaller linearity implies a more stable capacitance, which is desirable. In poly-to-poly capacitors, increasing doping concentration of the polysilicon electrodes of a capacitor reduces the voltage linearity of the capacitor. However, as the circuit density of VLSI circuits increases, high doping of polysilicon can result in an increased potential for a leakage current through the oxide. See, for example, T. Ono, T. Mori, T. Ajioka, T. Takayashiki, Studies of Thin Poly Si Oxides for E and E.sup.2 PROM, IEDM, 1985, pp. 380-383, and T. Iida, M. Nakahara, S. Gotoh and H. Akiba, Precise Capacitor Structure Suitable for Submicron Mixed Analog/Digital ASICs, Custom Integrated Circuits Conference, 1990, pp. 18.5.1-18.5.4. Additionally, the fabrication of poly-to-poly capacitors generally requires high temperature doping and oxidation steps, which can adversely affect reliability and performance of the integrated circuit components. Also, the metal-to-poly capacitor and the metal-to-polycide require additional processing steps which add to the complexity of the circuit and in many cases adversely affect reliability, or compromise performance. For poly-to-poly capacitors in which the top electrode is polycide, the capacitor has poor characteristics which require additional processing. The additional processing can be cost prohibitive